The field of art to which this invention pertains is aryl cyanate esters, i.e., cyanic acid esters of polyhydric phenols.
Industry is constantly searching for lighter, stronger and more resistant materials to be used in place of the materials used today. For example, the aerospace industry is devoting considerable effort to utilizing structural composites in place of metals. Structural composites based on thermoplastic or thermoset resins and glass or carbon fibers have been and are being used successfully in many parts of military and commercial aircraft. Thermoset resins which are being used in such applications are epoxy resins, bismaleimide resins, and cyanate ester resins.
Cyanate ester resins, which are finding increasing use in structural composites, adhesives and electrical grade insulation, are based on the reaction products of polyhydric phenols and cyanogen halides. Such resins and their methods of preparation are described in U.S. Pat. Nos. 3,403,128 and 3,755,042. Additional patents which describe cyanate esters are U.S. Pat. Nos. 3,987,230 and 4,330,658.
A process for preparing cyanate ester resins having improved purity is described in U.S. Pat. No. 4,028,393. In this process, di- or polytrialkyl ammonium phenolates are reacted with an excess of cyanogen halide in an organic solvent in the presence of a trialkyl amine.
In my copending U.S. patent application Ser. No. 581,778, filed Sep. 13, 1990, a process for preparing high purity bis(4-cyanatophenyl)-1,1-ethane is described. In this process, a solution of cyanogen halide in a halocarbon solvent is reacted with a solution of bis(4-hydroxyphenyl)-1,1-ethane and a tertiary amine in a halocarbon solvent at a temperature below -10.degree. C.
There is a need for a commercially acceptable process for manufacturing bis(4-cyanatophenyl)-1,1-ethane which uses environmentally acceptable solvents in the process.